Zoom lens and image pickup apparatus

ABSTRACT

A zoom lens made up of a first lens group having positive refracting power, a second lens group having negative refracting power, a third lens group having positive refracting power, and a fourth lens group having positive refracting power, which are disposed in order from an object side, in which the first lens group and the third lens groups are stationary, and the zoom lens performs mainly variable power by shifting the second lens group in an optical axis direction, and performs correction for image position fluctuations and focusing by shifting the fourth lens group in the optical axis direction, is characterized in that the first lens group is composed of five lenses: a concave lens; a convex lens with a strong convexity facing to an image side; a cemented lens made up of a concave lens with a strong concavity facing to the image side, and a convex lens; and a convex lens with a strong convexity facing to the object side, which are disposed in order from the object side, and by satisfying each of the following conditional expressions:
 
(1) 1.25&lt; h 1-4/ h 1-1&lt;1.55;
 
(2)  d 1-2/ d 1-3&lt;0.4;
 
(3) 1.65&lt;n1-2;
 
and
 
(4) 0.1&lt; H 1′/ f 1&lt;0.6.

TECHNICAL FIELD

The present invention relates to a novel zoom lens and, in particular,to a zoom lens suitable for a video camera or a digital still camera,and an image pickup apparatus using the same. Specifically, it relatesto a technique of providing a small zoom lens that, in obtaining a wideangle zoom lens, a lens of extremely simple construction is additionallysupplemented to an object side of a zoom lens based on a conventionaltechnique so as to strike a balance of aberration correction as a totalsystem, thereby suitably correcting various aberrations other thandistortion, and that has an extremely small front lens diameter, andalso providing an image pickup apparatus in which distortion due to theabove zoom lens is corrected to obtain an excellent image by processinga video signal obtained from an image pickup element.

BACKGROUND ART

In zoom lenses mainly used in consumer video cameras, a so-called fourgroup inner focus zoom system is the main stream, which has a four groupconfiguration in which refracting power arrangement is positive,negative, positive, and positive in order from an object side, wherein afirst lens group and a third lens group are stationary, and variablepower is mainly performed by shifting a second lens group in an opticalaxis direction, and correction for image position fluctuations andfocusing are performed by shifting a fourth lens group in the opticalaxis direction. As the configuration of the zoom lens related to thissystem, there have been proposed many different types, such as thosedescribed in Japanese Patent Application Laid-Open Nos. Hei 3-33710 andHei 4-153615.

In these lens configurations, the lens configurations of the first lensgroup and the second lens group employ a very similar lens type, so thatthe angle of view of a picked-up image diagonal at a wide angle end isabout 60 degrees at the utmost. For example, one described in JapanesePatent Application Laid-Open No. 2000-28922 attempts to achieveminiaturization of a front lens diameter by bringing an image sideprincipal point of the first lens group closer to the surface closest toan image side of the first lens group, but fails to achieve widening ofthe angle of view at a wide angle end to not less than 60 degrees, thusfailing to accomplish compatibility between widening of angle andminiaturization of the front lens diameter.

As an example of attempt to achieve sufficient widening of angle, thereis known one described in Japanese Patent Application Laid-Open No. Hei5-72475, which has developed the first lens group from a three-lensconfiguration into a five-lens configuration, on the basis of JapanesePatent Application Laid-Open No. Hei 3-33710.

There has also been proposed to correct a distortion that variesdepending on zooming (variable power) by an electric signal processingtechnique on an image pickup apparatus side. For example, JapanesePatent Application Laid-Open No. Hei 6-165024 is known.

In the zoom lens described in Japanese Patent Application Laid-Open No.Hei 5-72475, based on the lens type shown in Japanese Patent ApplicationLaid-Open No. Hei 3-33710, the inclination of a principal ray to thethird and later lenses of the first lens group is reduced to permitcorrection for various aberrations by disposing a concave lens and aconvex lens having large air spacing therebetween on the object side ofthe first lens group of the three-lens configuration, in order to add aconfiguration close to an afocal system, such as a wide conversion lens.

It is however necessary to dispose the added two lenses with large airspacing, in order to correct properly in balance the distortion of awide angle end that tends to increase due to widening of angle andmeridional curvature of field, so an increase in front lens diameter isunavoidable. Moreover, since the zoom lens is the invention made onlyfor the purpose of widening of angle of the lens configuration ofJapanese Patent Application Laid-Open No. Hei 3-33710, it is realized bystrictly regulating the lens configuration of the first lens groupthrough the fourth lens group. With regard to specifications such aszoom ratio and F-number, front lens diameter, total length, back focus,etc., an optimum lens configuration for the intended purpose is notalways obtainable.

The present invention has for its subject to provide a wide-angle zoomlens most suitable for various specifications, which enables suchwidening of angle that the angle of view at a wide angle end is not lessthan 60 degrees, by making a first lens group into a five-lensconfiguration different from Japanese Patent Application Laid-Open No.Hei 5-72475, in combination with many different variations of so-calledfour-group inner focus system zoom lens, and in which increase in frontlens diameter is minimized to achieve the harmonization between wideningof angle and miniaturization of front lens diameter, and many differenttypes of variations of conventional types are applied to a third lensgroup and a fourth lens group.

Further miniaturization is also enabled in the following manners thatdistortion, the correction for which inevitably becomes difficult byachieving the harmonization between widening of angle andminiaturization of front lens diameter, is corrected by a video signalprocessing, and that the ratio of the angle of view of a wide angle endto that of a telephoto end, obtainable from an image surface afterdistortion correction, is redefined as a zoom ratio, thereby reducingparaxial focal length ratio (general definition of zoom ratio). Thepresent invention has for its subject to provide an image pickupapparatus that permits miniaturization for a zoom ratio required, byactively and largely causing negative distortion at a wide angle end andpositive distortion at a telephoto end, so that the change in the angleof view after distortion correction is sufficiently greater for thechange in paraxial focal length.

DISCLOSURE OF THE INVENTION

To solve the above-mentioned subject, a zoom lens of the presentinvention is made up of a first lens group having positive refractingpower, a second lens group having negative refracting power, a thirdlens group having positive refracting power, and a fourth lens grouphaving positive refracting power, which are disposed in order from anobject side, wherein the first lens group and the third lens group arestationary, and the zoom lens performs mainly variable power (zooming)by shifting the second lens group in an optical axis direction, andperforms correction for image position fluctuations and focusing byshifting the fourth lens group in the optical axis direction, in which:

-   -   the first lens group is composed of five lenses: a concave lens;        a convex lens with a strong convexity facing to an image side; a        cemented lens made up of a concave lens with a strong concavity        facing to the image side, and a convex lens; and a convex lens        with a strong convexity facing to the object side, which are        disposed in order from the object side, and configured so as to        satisfy each of the following respective conditional expressions        (1), (2), (3), and (4):        1.25<h4-/h1-1<1.55  (1)        d1-2/d1-3<0.4  (2)        1.65<n1-2  (3)        0.1<H1′/f1<0.6  (4)        where:    -   f1is a focal length of the first lens group;    -   h1-i is a paraxial ray height in the i-th surface from the        object side, when allowing a paraxial ray parallel to an optical        axis to enter the first lens group;    -   d1-i is axial spacing from the i-th surface to the (i+1)-th        surface in the first lens group;    -   n1-i is a refractive index on a d-line of the i-th surface in        the first lens group; and    -   H1′ is spacing from a vertex of a surface closest to the image        side in the first lens group to an image side principal point in        the first lens group (“−” indicates the object side, and “+”        indicates the image side).

Therefore, in the zoom lens of the present invention, it is possible tocorrect various aberrations, and widening of angle and miniaturizationof front lens diameter are both satisfied.

An image pickup apparatus of the present invention comprises: a zoomlens; image pickup means converting an image captured by the zoom lensinto an electric image signal; and image control means. The imagecontrol means is configured so as to form a new image signal subjectedto coordinate conversion by shifting a point on an image defined by animage signal formed by the image pickup means, while referring to aconversion coordinate factor previously provided in response to avariable power rate through the zoom lens, and then output the new imagesignal. The zoom lens is made up of a first lens group having positiverefracting power, a second lens group having negative refracting power,a third lens group having positive refracting power, and a fourth lensgroup having positive refracting power, which are disposed in order froman object side. The first lens group and the third lens group arestationary, and the zoom lens performs mainly variable power by shiftingthe second lens group in an optical axis direction, and performscorrection for image position fluctuations and focusing by shifting thefourth lens group in the optical axis direction. The first lens group iscomposed of five lenses: a concave lens; a convex lens with a strongconvexity facing to an image side; a cemented lens made up of a concavelens with a strong concavity facing to the image side, and a convexlens; and a convex lens with a strong convexity facing to the objectside, which are disposed in order from the object side, and configuredso as to satisfy each of the following conditional expressions: (1)1.25<h1-4/h1-1<1.55; (2) d1-2/d1-3<0.4; (3) 1.65<n1-2; and (4)0.1<H1′/f1<0.6, where F1 is a focal length of the first lens group; h1-iis a paraxial ray height in the i-th surface from the object side whenallowing a paraxial ray parallel to an optical axis to enter the firstlens group; d1-i is axial spacing from the i-th surface to the (i+1)-thsurface in the first lens group; n1-i is a refractive index on a d lineof the i-th surface in the first lens group; and H1′ is spacing from avertex of a surface closest to the image side in the first lens group toan image side principal point in the first lens group (“−” indicates theobject side, and “+” indicates the image side).

Therefore, in the image pickup apparatus of the present invention,miniaturization for a zoom ratio required is enabled by actively andlargely causing negative distortion at a wide angle end and positivedistortion at a telephoto end, so that the change in the angle of viewafter distortion correction is sufficiently greater for the change inparaxial focal length.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic diagram showing a first preferred embodiment of azoom lens of the present invention, together with FIG. 2 to FIG. 4,which particularly shows a lens configuration;

FIG. 2 is a diagram showing spherical aberration, astigmatism anddistortion at a wide angle end;

FIG. 3 is a diagram showing spherical aberration, astigmatism anddistortion at a middle focal position between a wide angle end and atelephoto end;

FIG. 4 is a diagram showing spherical aberration, astigmatism anddistortion at a telephoto end;

FIG. 5 is a schematic diagram showing a second preferred embodiment of azoom lens of the present invention, together with FIG. 6 to FIG. 8,which particularly shows a lens configuration;

FIG. 6 is a diagram showing spherical aberration, astigmatism anddistortion at a wide angle end;

FIG. 7 is a diagram showing spherical aberration, astigmatism anddistortion at a middle focal position between a wide angle end and atelephoto end;

FIG. 8 is a diagram showing spherical aberration, astigmatism anddistortion at a telephoto end;

FIG. 9 is a schematic diagram showing a third preferred embodiment of azoom lens of the present invention, together with FIG. 10 to FIG. 12,which particularly shows a lens configuration;

FIG. 10 is a diagram showing spherical aberration, astigmatism anddistortion at a wide angle end;

FIG. 11 is a diagram showing spherical aberration, astigmatism anddistortion at a middle focal position between a wide angle end and atelephoto end;

FIG. 12 is a diagram showing spherical aberration, astigmatism anddistortion at a telephoto end;

FIG. 13 is a schematic diagram showing a fourth preferred embodiment ofa zoom lens of the present invention, together with FIG. 14 to FIG. 16,which particularly shows a lens configuration;

FIG. 14 is a diagram showing spherical aberration, astigmatism anddistortion at a wide angle end;

FIG. 15 is a diagram showing spherical aberration, astigmatism anddistortion at a middle focal position between a wide angle end and atelephoto end;

FIG. 16 is a diagram showing spherical aberration, astigmatism anddistortion at a telephoto end; and

FIG. 17 is a block diagram showing the configuration of a preferredembodiment of an image pickup apparatus of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

Preferred embodiments of a zoom lens and an image pickup apparatus ofthe present invention will be described below with reference to theaccompanying drawings. FIG. 1 to FIG. 4 show a first preferredembodiment. FIG. 5 to FIG. 8 show a second preferred embodiment. FIG. 9to FIG. 12 show a third preferred embodiment. FIG. 13 to FIG. 16 show afourth preferred embodiment.

Zoom lenses 1, 2, 3, and 4 according to the first to the fourthpreferred embodiments have, as shown in FIG. 1, FIG. 5, FIG. 9, and FIG.13, an optical system made up of: a first lens group Gr1 having positiverefracting power; a second lens group Gr2 that has negative refractingpower and is removable in an optical axis direction in order to mainlyperform zooming (variable power); a third lens group Gr3 having positiverefracting power; and a fourth lens group Gr4 that has positiverefracting power and is removable in an optical axis direction in orderto correct focal position fluctuations during zooming and also performfocusing, which are disposed in order from an object side.

The above respective zoom lenses 1, 2, 3, and 4 are different in therequirements of the configurations of the third lens group Gr3 and thefourth group lens Gr4. The requirements of the first lens group Gr1 andthe second lens group Gr2 are common to them.

In the zoom lenses 1, 2, 3, and 4, the first lens group Gr1 is made upof five lenses: a concave lens L1; a convex lens L2 with a strongconvexity facing to an image side; a cemented lens made up of a concavelens L3 with a strong concavity facing to the image side, and a convexlens L4; and a convex lens L5 with a strong convexity facing to theobject side, which are disposed in order from an object side, andsatisfies each of the following conditional expressions (1), (2), (3),and (4):(1) 1.25<h1-4/h1-1<1.55;(2) d1-2/d1-3<0.4;(3) 1.65<n1-2;and(4) 0.1<H1′/f1<0.6,where:

-   -   f1 is a focal length of the first lens group;    -   h1-i is a paraxial ray height in the i-th surface from the        object side when allowing a paraxial ray parallel to an optical        axis to enter the first lens group;    -   d1-i is axial spacing from the i-th surface to the (i+1)-th        surface in the first lens group;    -   n1-i is a refractive index on a d-line of the i-th lens in the        first lens group; and    -   H1′ is spacing from a vertex of a surface closest to the image        side in the first lens group to an image side principal point in        the first lens group (“−” indicates the object side, and “+”        indicates the image side).

The conditional expression (1) is to express the condition for enablingsufficient aberration correction even if a configuration close to aconventional case is applied to the lens configuration of the concavelens L3 and the later lenses by taking a configuration close to afocalby the use of the concave lens L1 and the convex lens L2, therebyreducing the inclination of a principal ray that enters the concave lensL3. Exceeding a lower limit may make it difficult to sufficiently reducethe inclination of the principal ray that enters the concave lens L3.Exceeding an upper limit may increase the synthetic thickness from theconcave lens L1 to the convex lens L2, and causes enlargement of frontlens dimension, thereby making it difficult to achieve miniaturizationof front lens diameter, which is an object of the present invention.

The conditional expression (2) is to express the condition forminiaturizing front lens diameter than a conventional case, whilesatisfying the conditional expression (1). When the inclination of aprinciple ray in the air spacing between the concave lens L1 and theconvex lens L2 is compared with the inclination of a principle ray inthe convex lens L2, the inclination of the principle ray at the time ofpassing within the convex lens L2 is smaller. Therefore, in order toobtain the same result by the conditional expression (1), it isadvantageous for miniaturization of front lens diameter, to narrow theabove mentioned air spacing and thicken the convex lens L2. Accordingly,it is prerequisite for achieving the object of the present invention toincrease the thickness of the convex lens L2 rather than the above airspacing. The lower limit of this conditional expression is an effectivediameter that is determined from an off-axis luminous flux passingthrough the most periphery of the concave lens L1, and is a valueenabling to configure so that the concave lens L1 and the convex lens L2come into contact with each other.

The conditional expression (3) is to express the condition forminiaturizing front lens diameter by further reducing the inclination ofthe principal ray within the convex lens L2. Exceeding a lower limit mayincrease the thickness of the convex lens L2 for satisfying theconditional expression (1). As a result, the front lens diameter may beenlarged.

The conditional expression (4) is to express the condition for providingthe first lens group Gr1 with a configuration suitable for achieving theharmonization between widening of angle and miniaturization of frontlens diameter, through the use of an approximately afocal configurationby the use of the concave lens L1 and the convex lens L2. A sufficienthigh variable power ratio can be obtained while satisfying both wideningof angle and miniaturization of front lens diameter, by defining therefracting power arrangement of the respective lenses such that theimage side principal point of the first lens group Gr1 is generated onthe sufficiently image side than the most image side surface of thefirst lens group Gr1.

In the zoom lenses 1, 2, 3, and 4, the second lens group Gr2 is composedof three lenses of a concave meniscus lens L6 with a strong concavityfacing to the image side, a double concave lens L7, and a convex lensL8, which are disposed in order from the object side, and satisfy theconditional expression (5):1.8<(n2-1+n2-2)/2,  (5)where:

-   -   n2-1 is a refractive index on a d-line of the concave meniscus        lens of the second lens group; and    -   n2-2 is a refractive index on a d-line of the double concave        lens of the second lens group.

The conditional expression (5) is to prevent that Petzval sum necessaryto the correction for curvature of field becomes too small. Theconfiguration of the first lens group Gr1 is like so-called retro focustype, in which the image side principal point protrudes to the imageside, so that the Petzval sum inherent in the first lens group Gr1 isplus and a small value. That contributes to letting Petzval sum of theoverall system be too small, but there is inevitability and that isunavoidable. To bring the Petzval sum of the overall system into anappropriate value, means that weakens the refracting power of the secondlens group Gr2, or means that increases the refracting power of theconcave lens of the second lens group Gr2 can be considered. However, ifthe refracting power of the second lens group Gr2 is weakened, theamount of movement of the second lens group Gr2 required for variablepower is increased to cause enlargement. It is therefore necessary tobring an average value of the refracting powers of the concave meniscuslens L6 and the double concave lens L7 of the second lens group Gr2,into one within the range of the conditional expression (5), so as tofacilitate the correction for curvature of field.

The zoom lenses 1, 2, 3, and 4 are different from one another in thecondition related to the configurations of the third lens group Gr3 andthe fourth group lens Gr4.

With regard to the configurations of the third lens group and the fourthlens group, the zoom lens 1 according to the first preferred embodimenthas the following configuration.

As can be seen from FIG. 1, the third lens group Gr3 is made up of asingle convex lens L9, and at least one surface is composed of anaspheric surface. The fourth lens group Gr4 is composed of a cementedlens made up of a concave meniscus lens L10 with a concavity facing toan image side, and a double convex lens L11 whose surface on the imageside is an aspheric surface,-which are disposed in order from an objectside. These satisfy the following respective conditional expressions(6), (7), and (8):−0.4<f3/r3-2<0.4;  (6)−1.25<r4-1/r4-3<−0.8;  (7)and0.3<−2/f4<0.6,  (8)where:

-   -   f3 is a focal length of the third lens group;    -   f4 is a focal length of the fourth lens group;    -   r3-2 is a radius of curvature of the image side surface of the        convex lens in the third lens group;    -   r4-1 is a radius of curvature of the object side surface of the        concave meniscus lens in the fourth lens group;    -   r4-2 is a radius of curvature of a cemented surface in the        fourth lens group; and    -   r4-3 is a radius of curvature of a surface on the image side of        the convex lens in the fourth lens group.

The conditional expression (6) is to define the shape of the an asphericsurface single convex lens L9 of the third lens group Gr3, and definethe condition related to the sensitivity with regard to the decentering(misalignment) at the time of forming an aspheric surface, and therelative decentering between the third lens group Gr3 and the fourthlens group Gr4. The decentering degree of both surfaces of an asphericsurface lens is determined depending on the decentering degree of amold. For example, a glass mold can cause decentering of about 10 μm.Moreover, when assembled in a lens-barrel, the relative decenteringbetween the third lens group Gr3 and the fourth lens group Gr4 can arisein an amount of about 20 μm. In order that the image quality of productscan sufficiently reproduce design performance even in the presence ofsuch an error, it is required to design so as to relax such sensitivitythat the decentering between the respective surfaces exerts on the imagequality. Exceeding an upper limit may increase such sensitivity that thedecentering between the respective surfaces exerts on the image quality,and the precision required for forming and assembling may exceed processcapability, thus making it difficult to mass-produce with stableperformance. Exceeding a lower limit may make it difficult to correctproperly in balance spherical aberration and curvature of field.

The conditional expression (7) relates to the decentering sensitivity ofthe fourth lens group Gr4. Exceeding a lower limit may result in thatthe positive refracting power of the fourth lens group Gr4 concentrateson a surface on the object side of the concave meniscus lens L10 (itsradius of curvature is r4-1), and aberration deterioration due to thedecentering and inclination of this surface becomes significant, thusmaking it difficult to stably reproduce design performance in massproduction. Even if the fourth lens group Gr4 has an error indecentering and inclination, the sensitivity that deterioratesaberration can also be dispersed by properly dispersing the positiverefracting power of the fourth lens group Gr4 into a surface on theobject side of the concave meniscus lens L10 and a surface on the imageside of the double convex lens L11 (its radius of curvature is r4-3).However, exceeding an upper limit may increase spherical aberrationgenerated from a surface on the image side of the double convex lensL11, and may render correction difficult.

The above conditional expression (8) relates to the correction for comaaberration and curvature of field. In the state that the radius ofcurvature r4-2 of the cemented surface between the concave meniscus lensL10 having negative refracting power and the double convex lens L11satisfies the conditional expression (7), if tried to determine a glassmaterial of the concave meniscus lens L10 and the double convex lensL11, so great degree of freedom of design cannot be obtained from thecondition for chromatic aberration correction. However, since theabove-mentioned cemented surface shape performs dominant operationrelated to the correction for coma aberration and curvature of field, itis required to select a glass material so as to satisfy the conditionalexpressions (7) and (8). Exceeding an upper limit may result in that,even when a great difference of refractive index between the concavemeniscus lens L10 and the double convex lens L11 is configured, thenegative refracting power of the cemented surface of both lenses (theconcave meniscus lens L10 and the double convex lens L11) becomes toosmall, thus making it difficult to correct an inward coma aberration andcurvature of field inclined to an under side. Exceeding a lower limitmay result in that the coma aberration of a color, in which a g-line isjumped outwardly on an upper ray side of an off-axis luminous flux,becomes significant and correction becomes difficult.

With regard to the configurations of the third lens group and the fourthlens group, the zoom lens 2 according to the second preferred embodimenthas the following configuration.

As can be seen from FIG. 5, in the zoom lens 2, a third lens group Gr3is composed of a convex lens G9, and a cemented lens made up of a convexlens G10 with a strong convexity facing to an object side, and a concavelens G11 with a strong concavity facing to an image side, which aredisposed in order from the object side, and at least one surface is anaspheric surface. A fourth lens group Gr4 is made up of a single convexlens G12, and at least one surface is an aspheric surface. These satisfyeach of the following conditional expressions (9) and (10):0.4<h3-5/h3-1<0.7;  (9)and0.75<f3/f3-1<1,  (10)where:

-   -   h3-i is a paraxial ray height in the i-th surface from the        object side of the third lens group Gr3, when allowing a        paraxial ray parallel to an optical axis to enter the first lens        group Gr1 at a wide angle end;    -   f3 is a focal length of the third lens group Gr3; and    -   f3-1 is a focal length of the single convex lens of the third        lens group Gr3.

The conditional expression (9) is to express the condition forshortening the total length by shortening the focal length of the fourthlens group Gr4. Exceeding an upper limit may result in failure to obtainsufficient effect of shortening the total length. Exceeding a lowerlimit may result in that Petzval sum becomes too small and thecorrection for curvature of field becomes difficult.

The above conditional expression (10) relates to the decenteringsensitivity of the convex lens G9 that is the first lens of the thirdlens group Gr3. In determining the refracting power arrangement of therespective surfaces of the third lens group Gr3 so as to satisfy theconditional expression (9), if too much burden of positive refractingpower is concentrated on the convex lens G9, when an error ofdecentering or inclination occurs in the convex lens G9, aberrationdeterioration becomes significant, and stable performance maintenance inmass production becomes difficult. It is therefore important to have theconvex lens G10, which is the second lens of the third lens group Gr3,share positive refracting power so as not to exceed the upper limit.Exceeding the lower limit may cause the need to increase the compositethickness of the convex lens G10 and the concave lens G11, whichconstitute the cemented lens of the third lens group Gr3, in order tosatisfy the conditional expression (9). Thus, even when back focus canbe shortened, the total length shortening cannot be attained, therebyfailing to achieve miniaturization that is an object of the presentinvention.

With regard to the configurations of the third lens group Gr3 and thefourth lens group Gr4, the zoom lens 3 according to the third preferredembodiment has the following configuration.

As can be seen from FIG. 9, a third lens group Gr3 is made up of asingle convex lens L9, and at least one surface is composed of anaspheric surface. A fourth lens group Gr4 is composed of a cemented lensmade up of a convex lens L10 with a convexity facing to an object side,a concave lens L11, and a convex lens L12, which are disposed in orderfrom the object side. Further, at least a surface closest to the objectside is an aspheric surface. These satisfy each of the followingconditional expressions (11) and (12):n4-2>1.8;  (11)and0.1<f3/f4<0.7,  (12)where:

-   -   n4-2 is a refractive index on a d-line of the concave lens of        the fourth lens group;    -   f3 is a focal length of the third lens group; and    -   f4 is a focal length of the fourth lens group.

The conditional expression (11) is to define a glass material of theconcave lens L11 of the fourth lens group Gr4. By increasing therefractive index, the curvature of the cemented surface between theconcave lens L10 and the convex lens L12 is relaxed, so that there arethe function of suppressing refraction fluctuations due to colorsrelating to chromatic aberration and spherical aberration, which are dueto movement of the fourth lens group Gr4, and the function of correctingPetzval sum toward the plus side, which is advantageous in correctingcurvature of field.

The conditional expression (12) relates to the focal lengths of thethird lens group Gr3 and the fourth lens group Gr4. Exceeding a lowerlimit may make it difficult to suppress spherical aberrationfluctuations, or cause the amount of movement of the fourth lens groupGr4 to increase, or the total length increases. Exceeding an upper limitmay increase aberration deterioration due to manufacturing error of thefourth lens group Gr4, which is unfavorable.

With regard to the configurations of the third lens group and the fourthlens group, the zoom lens 4 according to the fourth preferred embodimenthas the following configuration.

As can be seen from FIG. 13, in the zoom lens 4, a third lens group Gr3is composed of a convex lens G9, and a cemented lens made up of a convexlens G10 with a strong convexity facing to an object side, and a concavelens G11 with a strong concavity facing to an image side, which aredisposed in order from the object side, and at least one surface is anaspheric surface. A fourth lens group Gr4 is composed of a cemented lensmade up of a double convex lens L12, and a concave lens L13 with aconvexity facing to the image side, and at least one surface is anaspheric surface. These satisfy each of the following conditionalexpressions (9), (11), and (13):0.4<h3-5/h3-1<0.7;  (9)n4-2>1.8;  (11)and0.75<f3/f3-1<1.3,  (13)where:

-   -   h3-i is a paraxial ray height in the i-th surface from the        object side of the third lens group Gr3, when allowing a        paraxial ray parallel to an optical axis to enter the first lens        group Gr1 at a wide angle end;    -   f3 is a focal length of the third lens group Gr3;    -   f3-1 is a focal length of the single convex lens of the third        lens group Gr3; and    -   n4-2 is a refractive index on a d-line of the concave lens of        the fourth lens group.

The conditional expression (9) is to express the condition forshortening the total length by shortening the focal length of the fourthlens group Gr4. Exceeding an upper limit may result in failure to obtainsufficient effect of shortening the total length. Exceeding a lowerlimit may result in that Petzval sum becomes too small and thecorrection for curvature of field becomes difficult.

The conditional expression (11) is to define a glass material of theconcave lens L13 of the fourth lens group Gr4. By increasing therefractive index, the curvature of the cemented surface with the doubleconvex lens L12 is relaxed, so that there are the function ofsuppressing refraction fluctuations on chromatic aberration andspherical aberration due to the colors, which are due to movement of thefourth lens group Gr4, and the function of correcting Petzval sum towardthe plus side, which is advantageous in correcting curvature of field.

The conditional expression (13) relates to the decentering sensitivityof the convex lens L9 that is the first lens of the third lens groupGr3. In determining the refracting power arrangement of the respectivesurfaces of the third lens group Gr3 so as to satisfy the conditionalexpression (9), if too much burden of positive refracting power isconcentrated on the convex lens L9, when an error of decentering orinclination occurs in the convex lens L9, aberration deteriorationbecomes significant, and stable performance maintenance in massproduction becomes difficult. It is therefore important to have theconvex lens L10, which is the second lens of the third lens group Gr3,share the positive refracting power so as not to exceed the upper limit.Exceeding the lower limit may cause the need to increase the compositethickness of the convex lens L10 and the concave lens L11, whichconstitute the cemented lens of the third lens group Gr3, in order tosatisfy the conditional expression (9). Even when back focus can beshortened, shortening of the total length cannot be attained, therebyfailing to achieve miniaturization that is an object of the presentinvention.

FIG. 17 is a block diagram showing an example of the configuration of animage pickup apparatus 100 according to the present invention. In FIG.17, the numeral 101 indicates an image pickup lens capable of zooming,which is provided with a focus lens 101 a and a variator lens 101 b; 102indicates an image pickup element such as a CCD; 103 indicates an imagecontrol circuit for performing control of various operations, such ascorrecting distortion of an image; 104 indicates a first image memoryfor storing image data obtainable from the image pickup element 102; and105 indicates a second image memory for storing image data in whichdistortion has been corrected. The numeral 106 indicates a data tablefor storing distortion information; and 107 indicates a zoom switch forconverting an operator's zooming instruction into an electric signal.

For example, if the zoom lens 1, 2, 3, or 4 according to the aboverespective preferred embodiments is applied to the above image pickuplens 101, the focus lens 101 a corresponds to the fourth lens group Gr4,and the variator lens 101 b corresponds to the second lens group Gr2.

As shown in FIG. 2 through FIG. 4, FIG. 6 through FIG. 8, FIG. 10through FIG. 12, and FIG. 14 through FIG. 16, which are related to thedistortion of the image pickup lens 101, a distortion curve variesdepending on zooming. Consequently, the distortion fluctuations dependon the position of the variator lens 101 b. Hence, the data table 106stores conversion coordinate factors, which associate thetwo-dimensional position information of the first image memory 104 andthe second image memory 105 at certain positions of the variator lens101 b. Moreover, the position of the variator lens 101 b is divided intomany positions from a wide angle end to a telephoto end, and conversioncoordinate factors corresponding to their respective positions arestored in the data table 106.

If an operator operates the zoom switch 107 to shift the position of thevariator lens 101 b, the image control circuit 103 shifts the focus lens101 a to control such that focus is not blurred, and also receives theconversion coordinate factor corresponding to the position of thevariator lens 101 b, from the data table 106. When the position of thevariator lens 101 b does not correspond to any of previously dividedpositions, a proper conversion coordinate factor is obtained from theconversion coordinate factor for a position in the vicinity thereof withthe aid of processing, such as interpolation. The conversion coordinatefactors are factors for shifting the positions of points on an imagearranged discretely in two dimensions. With respect to an image betweenthe points arranged discretely, a shift-destination position is foundfrom processing, such as interpolation. The image control circuit 103corrects distortion by performing vertical and horizontal image shiftprocessing based on this conversion coordinate factor, to theinformation of the first image memory 104 obtained from the image pickupelement 102, and creates, in the second image memory 105, imageinformation in which the distortion has been corrected, and thenoutputs, as a video signal, a signal based on the image informationcreated in the second image memory 105.

Numerical value embodiments in the zoom lenses 1, 2, 3, and 4 accordingto the above respective preferred embodiments will next be described.

In the above zoom lenses 1, 2, and 4, a fixed diaphragm IR is positionedimmediately ahead of the third lens group Gr3, and a filter FL isinterposed between the fourth lens group Gr4 and an image surface IMG.In the zoom lens 3, a fixed diaphragm IR is positioned immediatelybehind the third lens group Gr3, and a filter FL is interposed betweenthe fourth lens group Gr4 and an image surface IMG.

In the following explanation, “si” indicates the i-th surface countingfrom an object side; “ri” indicates the radius of curvature of the i-thsurface “si” counting from the object side; “di” indicates axial spacingbetween the i-th surface “si” and the (i+1)-th surface “si+1”, countingfrom the object side; “ni” indicates a refractive index on a d-line(587.6 nm in wavelength) of the material constituting the i-th lens “Li”or “Gi”; “vi” indicates an Abbe number on the d-line of the materialconstituting the i-th lens “Li” or “Gi”; “nFL” indicates a refractiveindex on a d-line of a material constituting a filter F; “vFL” indicatesan Abbe number on the d-line of a material constituting the filter FL;“Fno” indicates an open F value (F-number); and “ω” indicates a halfangle of view.

An aspherical shape is to be defined by the following equation (Equation1):

${{xi} = {\frac{H^{2}}{{ri}\lbrack {1 + \sqrt{1 - \frac{H^{2}}{{ri}^{2}}}} \rbrack} + {\sum\;{A_{j}H^{j}}}}},$where “xi” represents a depth of the aspherical surface and “H”represents a height from the optical axis.

The respective values in the numerical value embodiments of the zoomlens 1 according to the first preferred embodiment are presented inTable 1.

TABLE 1 Si ri di ni vi s1 r1 = −20.136 d1 = 0.313 n1 = 1.88300 v1 = 40.8s2 r2 = 6.978 d2 = 0.587 s3 r3 = ∞ d3 = 2.577 n2 = 1.83481 v2 = 42.7 s4r4 = −6.794 d4 = 0.078 s5 r5 = 9.228 d5 = 0.215 n3 = 1.92286 v3 = 20.9s6 r6 = 3.996 d6 = 0.785 n4 = 1.51680 v4 = 64.2 s7 r7 = 59.327 d7 =0.078 s8 r8 = 3.907 d8 = 0.625 n5 = 1.83481 v5 = 42.7 s9 r9 = 68.355 d9= variable S10 r10 = 8.681 d10 = 0.176 n6 = 1.88300 v6 = 40.8 s11 r11 =1.765 d11 = 0.489 S12 r12 = −1.856 d12 = 0.156 n7 = 1.88300 v7 = 40.8S13 r13 = 1.728 d13 = 0.479 n8 = 1.92286 v8 = 20.9 S14 r14 = −9.711 d14= variable S15 r15 = ∞ d15 = 0.692 (diaphragm) S16 r16 = 2.762 d16 =0.794 n9 = 1.51680 v9 = 64.2 s17 r17 = −21.701 d17 = variable s18 r18 =2.823 d18 = 0.156 n10 = 1.92286 v10 = 20.9 s19 r19 = 1.698 d19 = 1.110n11 = 1.51680 v11 = 64.2 s20 r20 = −3.111 d20 = variable s21 r21 = ∞ d21= 0.809 nFL = 1.51680 vFL = 64.2 (filter) s22 r22 = ∞ d22 = 0.313(filter) (Back Focus)

Both surfaces s16, s17 of the single convex lens L9 of the third lensgroup Gr3, and a surface s20 on the image side of the double convex lensL11 of the fourth lens group Gr4 are formed in an aspheric surface. Thefourth-order, sixth-order, and eighth-order aspheric surface factors A4,A6, and A8 of the above respective surfaces s16, s17, and s20 arepresented in Table 2.

TABLE 2 Aspheric surface factor A4 A6 A8 s16 −0.7793 × 10⁻² −0.8078 ×10⁻² −0.8211 × 10⁻³ s17 +0.6459 × 10⁻² −0.8733 × 10⁻² −0.8647 × 10⁻³ s20+0.1245 × 10⁻¹ +0.8698 × 10⁻³ −0.8647 × 10⁻³

In the zoom lens 1, axial spacing d9, d14, d17, and d20 vary dependingon zooming. Focal length, F number Fno, angle of field (2ω), and axialspacing d9, d14 d17, d20 in a wide angle end, a middle focal position,and a telephoto end are presented in Table 3.

TABLE 3 Wide angle Middle focal Telephoto end position end Focal length1.00 3.42 5.40 Fno 1.85 2.20 2.54 Angle of 78.0 22.6 14.28 field(2ω) d90.156 2.108 2.677 D14 2.780 0.829 0.260 D17 1.250 0.597 0.898 D20 2.2312.884 2.583

FIG. 2 through FIG. 4 illustrate the spherical aberration, thedistortion, and the astigmatism of the zoom lens 1 in the abovenumerical value embodiments. In the spherical aberration diagram, thesolid line indicates the value of an e-line; the broken line indicatesthe value of a g-line (435.8 nm in wavelength); and the alternate longand short dash line indicates the value of a C-line (656.3 nm inwavelength). In the astigmatism diagram, the solid line indicates thevalue of sagittal image surface distortion; and the broken lineindicates the value of meridional image surface distortion.

Next, the values of the respective conditional expressions (1) through(8) in the above numerical value embodiments of the zoom lens 1 areshown in the following.(1) h1-4/h1-1=1.3485(2) d1-2/d1-3=0.228(3) n1-2=1.83481(4) H1′/f1=0.2477, f1=3.953(5) (n2-1+n2-2)/2=1.88300(6) f3/r3-2=−0.221, f3=4.794(7) r4+1/r4-3=−0.9076(8) r4-2/f4=0.4151, f4=4.091

The respective values in the numerical value embodiments of the zoomlens 2 according to the second preferred embodiment are presented inTable 4.

TABLE 4 Si ri di ni vi s1 r1 = −14.698 d1 = 0.333 n1 = 1.88300 v1 = 40.8s2 r2 = 6.801 d2 = 0.561 s3 r3 = ∞ d3 = 3.149 n2 = 1.85000 v2 = 43.0 s4r4 = −6.319 d4 = 0.078 s5 r5 = −71.436 d5 = 0.254 n3 = 1.92286 v3 = 20.9s6 r6 = 8.047 d6 = 0.781 n4 = 1.69680 v4 = 55.5 s7 r7 = −11.279 d7 =0.078 s8 r8 = 3.875 d8 = 0.679 n5 = 1.77250 v5 = 49.6 s9 r9 = 18.782 d9= variable s10 d10 = 10.076 d10 = 0.176 n6 = 1.88300 v6 = 40.8 s11 r11 =1.918 d11 = 0.500 s12 r12 = −2.091 d12 = 0.156 n7 = 1.88300 v7 = 40.8s13 r13 = 1.666 d13 = 0.490 n8 = 1.92286 v8 = 20.9 s14 r14 = −12.657 d14= variable s15 r15 = ∞ d15 = 0.589 (diaphragm) s16 r16 = 3.728 d16 =0.693 n9 = 1.77310 v9 = 47.2 s17 r17 = −9.413 d17 = 0.078 s18 r18 =2.116 d18 = 1.747 n10 = 1.51680 v10 = 64.2 s19 r19 = −3.404 d19 = 0.157n11 = 1.92286 v11 = 20.9 s20 r20 = 2.019 d20 = variable s21 R21 = 1.829d21 = 0.753 n12 = 1.58313 v12 = 59.5 s22 r22 = −4.055 d22 = variable s23r23 = ∞ d23 = 0.810 nFL = 1.51680 vFL = 64.2 (filter) s24 r24 = ∞ d24 =0.313 (filter) (Back Focus)

A surface s16 of the convex lens G9 of the third lens group Gr3, andboth surfaces s21, s22 of the single convex lens G12 of the fourth lensgroup Gr4 are formed in an aspheric surface. The fourth-order,sixth-order, and eighth-order aspheric surface factors A4, A6, and A8 ofthe above respective surfaces s16, s21, and s22 are presented in Table5.

TABLE 5 Aspheric surface factor A4 A6 A8 s16 −0.4018 × 10⁻² +0.6566 ×10⁻³ −0.9748 × 10⁻⁴ s21 −0.3153 × 10⁻¹ 0 0 s22 +0.2686 × 10⁻¹ 0 +0.2388× 10⁻²

In the zoom lens 2, axial spacing d9, d14, d20 and d22 vary depending onzooming. Focal length, F-number Fno, angle of field (2ω), and axialspacing d9, d14, d20, d22 in a wide angle end, a middle focal positionand a telephoto end are presented in Table 6.

TABLE 6 Wide angle Middle focal Telephoto end position end Focal length1.00 2.89 5.32 Fno 1.85 2.21 2.70 Angle of 78.4 26.4 14.12 field(2ω) d90.176 1.969 2.745 D14 2.899 1.107 0.330 D20 0.840 0.350 0.841 D22 0.6341.124 0.634

FIG. 6 through FIG. 8 illustrate the spherical aberration, thedistortion and the astigmatism of the zoom lens 2 in the above numericalvalue embodiments. In the spherical aberration diagram, the solid lineindicates the value of an e-line; the broken line indicates the value ofa g-line (435.8 nm in wavelength); and the alternate long and short dashline indicates the value of a C-line (656.3 nm in wavelength). In theastigmatism diagram, the solid line indicates the value of sagittalimage surface distortion; and the broken line indicates the value ofmeridional image surface distortion.

Next, the values of the respective conditional expressions (1) through(5), (9) and (10) in the above numerical value embodiments of the zoomlens 2 are shown in the following.(1) h1-4/h1-1=1.4461(2) d1-2/d1-3=0.178(3) n1-2=1.83500(4) H1′/f1=0.3488, f1=3.705(5) (n2-1+n2-2)/2=1.88300(8) h3-5/h3-1=0.533(9) f3/f3-1=−0.843, f3=2.981The respective values in the numerical value embodiments of the zoomlens 3 according to the third preferred embodiment are presented inTable 7.

TABLE 7 Si ri di ni vi s1 r1 = −28.4470 d1 = 0.8 n1 = 1.88300 v1 = 40.8s2 r2 = 23.1427 d2 = 1.6311 s3 r3 = ∞ d3 = 7.1580 n2 = 1.83481 v2 = 42.7s4 r4 = −16.6167 d4 = 0.3103 s5 r5 = 22.9139 d5 = 0.6 n3 = 1.84666 v3 =23.8 s6 r6 = 11.9511 d6 = 1.9324 n4 = 1.58913 v4 = 61.2 s7 r7 = 35.9589d7 = 0.1 s8 r8 = 11.7395 d8 = 1.9198 n5 = 1.69350 v5 = 53.3 s9 r9 =79.5152 d9 = variable s10 r10 = 9.8681 d10 = 0.6 n6 = 1.88300 v6 = 40.8s11 r11 = 4.0479 d11 = 1.7056 s12 r12 = −4.6659 d12 = 0.6353 n7 =1.77250 v7 = 49.6 s13 r13 = 4.4788 d13 = 1.1190 n8 = 1.84666 v8 = 23.8s14 r14 = 741.4375 d14 = variable s15 r15 = 7.8454 d15 = 1.3359 n9 =1.58313 v9 = 59.5 s16 r16 = −78.4964 d16 = 1.0464 s17 r17 = ∞ d17 =variable (diaphragm) s18 r18 = 8.6702 d18 = 0.7772 n10 = 1.58313 v10 =59.5 s19 r19 = ∞ d19 = 0.55 n11 = 1.84666 v11 = 23.8 s20 r20 = 6.1465d20 = 1.6626 n12 = 1.69680 v12 = 55.5 s21 r21 = −7.7211 d21 = variables22 r22 = ∞ d22 = 0.81 nFL = 1.51680 vFL = 64.2 (filter) s23 r23 = ∞ d23= 0.3 (filter) (Back Focus)

A surface s8 on an object side of the convex lens L5 of the first lensgroup Gr1, a surface s15 on the object side of the single convex lens L9of the third lens group Gr3, and a surface s18 on the object side of theconvex lens L10 of the fourth lens group Gr4 are formed in an asphericsurface. The fourth-order, sixth-order, eighth-order and tenth-orderaspheric surface factors A4, A6, A8, and A10 of the above respectivesurfaces s8, s15, and s18 are presented in Table 8.

TABLE 8 Aspheric surface factor A4 A6 A8 A10 s8 −0.54 × 10⁻³ 0.18 × 10⁻⁶−0.62 × 10⁻⁸ 0.12 × 10⁻⁹ s15 −0.33 × 10⁻³ −0.68 × 10⁻⁴     0.86 × 10⁻⁵−0.48 × 10⁻⁶   s18 −0.15 × 10⁻² 0.37 × 10⁻⁴ −0.82 × 10⁻⁵ 0.58 × 10⁻⁶

In the zoom lens 3, axial spacing d9, d14, d17, and d21 vary dependingon zooming. Focal length, F-number Fno, angle of field (2ω), and axialspacing d9, d14, d17, d21 in a wide angle end, a middle focal positionand a telephoto end are presented in Table 9.

TABLE 9 Wide angle Middle focal Telephoto end position end Focal length1.66 5.24 16.57 Fno 1.75 1.93 2.07 Angle of 76.2 24.2 7.7 field(2ω) d90.6695 7.2471 11.3733 D14 11.5083 4.9262 0.8 D17 3.6681 1.9519 1.4864D21 4.8648 6.5809 7.0464

FIG. 10 through FIG. 12 illustrate the spherical aberration, thedistortion and the astigmatism of the zoom lens 3 in the above numericalvalue embodiments. In the spherical aberration diagram, the solid lineindicates the value of an e-line; the broken line indicates the value ofa g-line (435.8 nm in wavelength); and the alternate long and short dashline indicates the value of a C-line (656.3 nm in wavelength). In theastigmatism diagram, the solid line indicates the value of sagittalimage surface distortion; and the broken line indicates the value ofmeridional image surface distortion.

Next, the values of the respective conditional expressions (1) through(5), (11) and (12) in the above numerical value embodiments of the zoomlens 3 are shown in the following.(1) h1-4/h1-1=1.400(2) d1-2/d1-3=0.228(3) n1-2=1.835(4) H1′/f1=0.265(5) (n2-1+n2-2)/2=1.828(11) n4-2=1.847(12) f3/f4=0.65

The respective values in the numerical value embodiments of the zoomlens 4 according to the fourth preferred embodiment are presented inTable 10.

TABLE 10 Si ri di ni vi s1 r1 = −134.7480 d1 = 0.9 n1 = 1.88300 v1 =40.8 s2 r2 = 14.0169 d2 = 2.8277 s3 r3 = ∞ d3 = 7.2 n2 = 1.83481 v2 =42.7 s4 r4 = −21.7936 d4 = 0.3 s5 r5 = 31.7581 d5 = 0.9 n3 = 1.84666 v3= 23.8 s6 r6 = 12.3060 d6 = 2.85 n4 = 1.69680 v4 = 55.5 s7 r7 = 35 d7 =0.3 s8 r8 = 14.4794 d8 = 2.4486 n5 = 1.80420 v5 = 46.5 s9 r9 = −153.0462d9 = variable s10 r10 = −72.8852 d10 = 0.7 n6 = 1.834 v6 = 37.3 s11 r11= 4.6392 d11 = 1.5177 s12 r12 = −6.4592 d12 = 0.4 n7 = 1.77250 v7 = 49.6s13 r13 = 4.3151 d13 = 1.4199 n8 = 1.84666 v8 = 23.8 s14 r14 = −36.2647d14 = variable s15 r15 = ∞ d15 = 1.0326 (diaphragm) s16 r16 = 9.6975 d16= 1.2318 n9 = 1.80610 v9 = 40.7 s17 r17 = −991.6604 d17 = 0.2855 s18 r18= 9.2949 d18 = 2.5216 n10 = 1.58144 v10 = 40.9 s19 r19 = −75.9863 d19 =0.7988 n11 = 1.84666 v11 = 23.8 s20 r20 = 7.4277 d20 = variable s21 r21= 10.7553 d21 = 2.1939 n12 = 1.58913 v12 = 61.2 s22 r22 = −4.8461 d22 =0.7 n13 = 1.80518 v13 = 25.5 s23 r23 = −7.8609 d23 = variable s24 r24 =∞ d24 = 0.81 nFL = 1.51680 vFL = 64.2 (filter) s25 r23 = ∞ d25 = 0.3(filter) (Back Focus)

A surface s17 on the image side of the convex lens L9 of the third lensgroup Gr3, and the surface s21 on the object side of the double convexlens L12 of the fourth lens group Gr4 are formed in an aspheric surface.The fourth-order, sixth-order, eighth-order, and tenth-order asphericsurface factors A4, A6, A8, and A10 of the above respective surfaces s17and s21 are presented in Table 11.

TABLE 11 Aspheric surface factor A4 A6 A8 A10 s17   0.17 × 10⁻³   0.44 ×10⁻⁵ −0.25 × 10⁻⁶   0.51 × 10⁻⁸ s21 −0.60 × 10⁻³ −0.29 × 10⁻⁵   0.98 ×10⁻⁶ −0.48 × 10⁻⁷

In the zoom lens 4, axial spacing d9, d14, d20, and d23 vary dependingon zooming. Focal length, F-number Fno, angle of field (2ω), and axialspacing d9, d14, d20, d23 in a wide angle end, a middle focal positionand a telephoto end are presented in Table 12.

TABLE 12 Wide angle Middle focal Telephoto end position end Focal length2.31 7.23 22.61 Fno 1.78 2.14 2.86 Angle of 78.0 25.0 8.4 field(2ω) d90.8719 7.3280 11.4029 D14 11.8310 5.3749 1.3 D20 5.5386 2.3561 1.2019D23 7.5197 10.7022 11.8565

FIG. 14 through FIG. 16 illustrate the spherical aberration, thedistortion and the astigmatism of the zoom lens 4 in the above numericalvalue embodiments. In the spherical aberration diagram, the solid lineindicates the value of an e-line; the broken line indicates the value ofa g-line (435.8 nm in wavelength); and the alternate long and short dashline indicates the value of a C-line (656.3 nm in wavelength). In theastigmatism diagram, the solid line indicates the value of sagittalimage surface distortion; and the broken line indicates the value ofmeridional image surface distortion.

Next, the values of the respective conditional expressions (1) through(5), (9), (11) and (13) in the above numerical value embodiments of thezoom lens 4 are shown in the following.(1) h1-4/h1-1=1.400(2) d1-2/d1-3=0.393(3) n1-2=1.835(4) H1′/f1=0.277(5) (n2-1+n2-2)/2=1.803(9) h3-5/h3-1=0.771(11) n4-2=1.805(13) f3/f3-1=1.261

All of the shapes and numerical values of the respective partsillustrated in the above-mentioned preferred embodiments are shownmerely by way of example of implementation performed when putting thepresent invention into practice, and the technical scope of the presentinvention should not be interpreted restrictively by these.

As apparent from the foregoing description, a zoom lens of the presentinvention (1) made up of a first lens group having positive refractingpower, a second lens group having negative refracting power, a thirdlens group having positive refracting power, and a fourth lens grouphaving positive refracting power, which are disposed in order from anobject side, wherein the first lens group and the third lens group arestationary, and the zoom lens performs mainly variable power by shiftingthe second lens group in an optical axis direction, and performscorrection for image position fluctuations and focusing by shifting thefourth lens group in the optical axis direction, is characterized bythat the first lens group is composed of five lenses: a concave lens; aconvex lens with a strong convexity facing to an image side; a cementedlens made up of a concave lens with a strong concavity facing to theimage side and a convex lens; and a convex lens with a strong convexityfacing to the object side, which are disposed in order from the objectside, and configured so as to satisfy the following conditionalexpressions:1.25<h1-4/h1-1<1.55;  (1)d1-2/d1-3<0.4;   (2)1.65<n1-2;   (3)and0.1<H1′/f1<0.6,   (4)where f1 is a focal length of the first lens group; h1-i is a paraxialray height in the i-th surface from the object side when allowing aparaxial ray parallel to an optical axis to enter the first lens group;d1-i is axial spacing from the i-th surface to the (i+1)-th surface inthe first lens group; n1-i is a refractive index on a d-line of the i-thlens in the first lens group; and H1′ is spacing from a vertex of asurface closest to the image side in the first lens group to a principalpoint on the image side in the first lens group (“−” indicates theobject side, and “+” indicates the image side).

Therefore, the zoom lens of the present invention enables to correctvarious aberrations and also achieve the compatibility between wideningof angle and miniaturization of front lens diameter. For example, in theperformance in which zoom ratio is approximately ten times, the angle ofview of a wide angle end exceeds 76 degrees, and the F-number of thewide angle end is approximately F1.7 to F1.8, it is possible toaccomplish such extreme miniaturization that the front lens diameter isapproximately five to seven times of diagonal dimension.

In the present invention (2), a second lens group is composed of threelenses: a concave meniscus lens with a strong concavity facing to animage side; and a cemented lens made up of a double concave lens and aconvex lens, which are disposed in order from the object side, andconfigured so as to satisfy the conditional expression:1.8<(n2-1+n2-2)/2,  (5)where n2-1 is a refractive index on a d-line of the concave meniscuslens of the second lens group; and n2-2 is a refractive index on ad-line of the double concave lens of the second lens group. Therefore,by preventing Petzval sum from being too small, the Petzval sum can beoptimized, and the correction for curvature of field is facilitated,thereby enabling to obtain an excellent image.

In the present inventions (3) and (4), a third lens group made up of asingle convex lens and at least one surface is an aspheric surface. Afourth lens group is composed of a cemented lens made up of a concavemeniscus lens with a concavity facing to an image side, and a doubleconvex lens, a surface on the image side of which is an asphericsurface, which are disposed in order from the object side. These areconfigured so as to satisfy the following respective conditionalexpressions:−0.4<f3/r3-2<0.4;  (6)−1.25<r4-1/r4-3<−0.8;  (7)and0.3<r4-2/f4<0.6,  (8)where f3 is a focal length of the third lens group; f4 is a focal lengthof the fourth lens group; r3-2 is a radius of curvature of a surface onthe image side of the convex lens in the third lens group; r4-1 is aradius of curvature of a surface on the object side of the concavemeniscus lens in the fourth lens group; r4-2 is a radius of curvature ofa cemented surface in the fourth lens group; and r4-3 is a radius ofcurvature of a surface on the image side of the convex lens in thefourth lens group. Therefore, coma aberration, spherical aberration andcurvature of field can be corrected properly in balance, and further,such sensitivity that the decentering between the respective lens andbetween the lens groups affects image quality can be relaxed to permitmass production with stable performance.

In the present inventions (5) and (6), a third lens group is composed ofa convex lens and a cemented lens made up of a convex lens with a strongconvexity facing to an object side and a concave lens with a strongconcavity facing to an image side, which are disposed in order from theobject side, and at least one surface is an aspheric surface. A fourthlens group is made up of a single convex lens, and at least one surfaceis an aspheric surface. These are configured so as to satisfy thefollowing respective conditional expressions:0.4<h3-5/h3-1<0.7;  (9)and0.75<f3/f3-1<1,  (10)where h3-i is a paraxial ray height in the i-th surface from the objectside of the third lens group, when allowing a paraxial ray parallel toan optical axis to enter the first lens group at a wide angle end; f3 isa focal length of the third lens group; and f3-1 is a focal length ofthe single convex lens of the third lens group. Therefore, the totallength can be shortened while suitably correcting various aberrations,thereby contributing to miniaturization.

In the present inventions (7) and (8), a third lens group is made up ofa single convex lens, and at least one surface is an aspheric surface. Afourth lens group is composed of a cemented lens made up of a convexlens with a convexity facing to an object side, a concave lens, and aconvex lens, which are disposed in order from the object side. Further,at least a surface closest to the object side is an aspheric surface.These are configured so as to satisfy the following respectiveconditional expressions:n4-2>1.8;  (11)and0.1<f3/f4<0.7,  (12)where n4-2 is a refractive index on a d-line of the concave lens of thefourth lens group; f3 is a focal length of the third lens group; and f4is a focal length of the fourth lens group. Therefore, effectivecorrection for curvature of field is enabled by suppressing refractionfluctuations due to colors relating to chromatic aberration andspherical aberration, which are due to movement of the fourth lensgroup, and by correcting Petzval sum toward the plus side. Also, theoverall system of a zoom lens can be minimized while suppressingspherical aberration fluctuations, without causing performancedeterioration. In addition, it is possible to relax the performancedeterioration due to manufacturing tolerance of the fourth lens group.

In the present inventions (9) and (10), a third lens group is composedof a convex lens and a cemented lens made up of a convex lens with astrong convexity facing to an object side and a concave lens with astrong concavity facing to an image side, which are disposed in orderfrom the object side, and at least one surface is an aspheric surface. Afourth lens group is composed of a cemented lens made up of a doubleconvex lens and a concave lens having a convexity on the image side, andat least one surface is an aspheric surface. These are configured so asto satisfy the following respective conditional expressions:0.4<h3-5/h3-1<0.7;  (9)n4-2>1.8;  (11)and0.75<f3/f3-1<1.3,  (13)where h3-i is a paraxial ray height in the i-th surface from the objectside of the third lens group Gr3, when allowing a paraxial ray parallelto an optical axis to enter the first lens group Gr1 at a wide angleend; f3 is a focal length of the third lens group Gr3; f3-1 is a focallength of the single convex lens of the third lens group Gr3; and n4-2is a refractive index on a d-line of the concave lens of the fourth lensgroup. Therefore, the total length can be shortened for miniaturization,while suitably correcting various aberrations.

An image pickup apparatus of the present invention (11) comprises: azoom lens; image pickup means for converting an image captured by thezoom lens into an electric image signal; and image control means. Theimage control means is configured so as to form a new image signalsubjected to coordinate conversion by shifting a point on an imagedefined by an image signal formed by the image pickup means, whilereferring to a conversion coordinate factor previously provided inresponse to a variable power rate through the zoom lens, and output thenew image signal. The zoom lens is made up of a first lens group havingpositive refracting power, a second lens group having negativerefracting power, a third lens group having positive refracting power,and a fourth lens group having positive refracting power, which aredisposed in order from the object side. The first lens group and thethird lens group are stationary, and the zoom lens performs mainlyvariable power by shifting the second lens group in an optical axisdirection, and performs correction for image position fluctuations andfocusing by shifting the fourth lens group in the optical axisdirection. The first lens group is composed of five lenses: a concavelens; a convex lens with a strong convexity facing to an image side; acemented lens made up of a concave lens with a strong concavity facingto the image side, and a convex lens; and a convex lens with a strongconvexity facing to the object side, which are disposed in order fromthe object side. These are characterized by arranging so as to satisfythe following respective conditional expressions:1.25<h1-4/h1-1<1.55;  (1)1-2/d1-3<0.4;  (2)1.65<n1-2;  (3)and0.1<H1′/f1<0.6,  (4)where f1 is a focal length of the first lens group; h1-i is a paraxialray height in the i-th surface from the object side when allowing aparaxial ray parallel to an optical axis to enter the first lens group;d1-i is axial spacing from the i-th surface to the (i+1)-th surface inthe first lens group; n1-i is a refractive index on a d-line of the i-thlens in the first lens group; and H1′ is spacing from a vertex of asurface closest to the image side in the first lens group to a principalpoint on the image side in the first lens group (“−” indicates theobject side, and “+” indicates the image side).

Therefore, in the image pickup apparatus of the present invention (11),by actively and largely causing negative distortion at a wide angle endand positive distortion at a telephoto end, the shifts in the angle ofview after distortion correction can be sufficiently greater for theshifts in paraxial focal length, thereby permitting miniaturization fora zoom ratio required.

In the present invention (12), the use of the zoom lens of the presentinvention (2) enables to prevent Petzval sum from being too small, andfacilitate the correction for curvature of field.

In the present inventions (13) and (14), by using the zoom lens of thepresent inventions (3) and (4), coma aberration, spherical aberration,and curvature of field can be corrected properly in balance, andfurther, such sensitivity that the decentering between the respectivelens and between the lens groups affects image quality can be relaxed topermit mass production with stable performance.

In the present inventions (15) and (16), by using the zoom lens of thepresent inventions (5) and (6), the total length can be shortened tocontribute to miniaturization, while suitably correcting variousaberrations.

In the present inventions (17) and (18), the refraction fluctuations dueto colors relating to chromatic aberration and spherical aberration,which are due to movement of the fourth lens group, can be suppressed byusing the zoom lens of the present inventions (7) and (8). By correctingPetzval sum toward the plus side, the effective correction for curvatureof field is enabled, and the miniaturization of the overall system ofthe zoom lens is also enabled without causing performance deterioration.In addition, it is possible to relax the performance deterioration dueto manufacturing tolerance of the fourth lens group.

In the present inventions (19) and (20), by using the zoom lens of thepresent inventions (9) and (10), the total length can be shortened forminiaturization, while suitably correcting various aberrations.

1. A zoom lens consisting of a first lens group having positiverefracting power, a second lens group having negative refracting power,a third lens group having positive refracting power, and a fourth lensgroup having positive refracting power, which are disposed in order froman object side, wherein the first lens group and the third lens groupsare stationary, and the zoom lens performs mainly variable power byshifting the second lens group in an optical axis direction, andperforms correction for image position fluctuations and focusing byshifting the fourth lens group in the optical axis direction,characterized in that: said first lens group is composed of five lenses:a concave lens; a convex lens with a strong convexity facing to an imageside; a cemented lens composed of a concave lens with a strong concavityfacing to the image side, and a convex lens; and a convex lens with astrong convexity facing to the object side, which are disposed in orderfrom the object side, and is configured so as to satisfy each of thefollowing conditional expressions:(1) 1.25<h1-4/h1-1<1.55;(2) d1-2/d1-3<0.4;(3) 1.65<n1-2;and(4) 0.1<H1′/f1<0.6, where: f1 is a focal length of the first lens group;h1-i is a paraxial ray height in the i-th surface from the object sidewhen allowing a paraxial ray parallel to an optical axis to enter thefirst lens group; d1-i is axial spacing from the i-th surface to the(i+1)-th surface in the first lens group; n1-i is a refractive index ona d-line of the i-th lens in the first lens group; and H1′ is spacingfrom a vertex of a surface closest to the image side in the first lensgroup to a principal point on the image side in the first lens group(“−” indicates the object side, and “+” indicates the image side). 2.The zoom lens as claimed in claim 1, characterized in that the secondlens group is composed of three lenses of a concave meniscus lens with aconcavity facing to the image side, a double concave lens and a convexlens, which are disposed in order from the object side, andcharacterized by satisfying the following conditional expression (5):1.8<(n2-1+n2-2)/2,  (5) where: n2-1 is a refractive index on a d-line ofthe concave meniscus lens of the second lens group; and n2-2 is arefractive index on a d-line of the double concave lens of the secondlens group.
 3. The zoom lens as claimed in claim 1, characterized inthat: the third lens group is composed of a single convex lens, and atleast one surface is an aspheric surface; and the fourth lens group iscomposed of a cemented lens made up of a concave meniscus lens with aconcavity facing to the image side, and a double convex lens whosesurface on the image side is an aspheric surface, which are disposed inorder from the object side, and characterized by satisfying each of thefollowing conditional expressions (6), (7), and (8):−0.4<f3/r3-2<0.4;  (6)−1.25<r4-1/r4-3<−0.8;  (7)and0.3<r4-2/f4<0.6,  (8) where: f3 is a focal length of the third lensgroup; f4 is a focal length of the fourth lens group; r3-2 is a radiusof curvature of the image side surface of the convex lens of the thirdlens group; r4-1 is a radius of curvature of the object side surface ofthe concave meniscus lens of the fourth lens group; r4-2 is a radius ofcurvature of a cemented surface of the fourth lens group; and r4-3 is aradius of curvature of a surface on the image side of the convex lens ofthe fourth lens group.
 4. The zoom lens as claimed in claim 2,characterized in that: the third lens group is composed of a singleconvex lens, and at least one surface is an aspheric surface; and thefourth lens group is composed of a cemented lens made up of a concavemeniscus lens with a concavity facing to the image side, and a doubleconvex lens whose surface on the image side is an aspheric surface,which are disposed in order from the object side, and characterized bysatisfying each of the following conditional expressions (6), (7), and(8):−0.4<f3/r3-2<0.4;  (6)−1.25<r4-1/r4-3<−0.8;  (7) and0.3<r4-2/f4<0.6,  (8) where: f3 is a focal length of the third lensgroup; f4 is a focal length of the fourth lens group; r3-2 is a radiusof curvature of the image side surface of the convex lens of the thirdlens group; r4-1 is a radius of curvature of the object side surface ofthe concave meniscus lens of the fourth lens group; r4-2 is a radius ofcurvature of a cemented surface of the fourth lens group; and r4-3 is aradius of curvature of a surface on the image side of the convex lens ofthe fourth lens group.
 5. The zoom lens as claimed in claim 1,characterized in that: the third lens group is composed of a convexlens, and a cemented lens made up of a convex lens with a strongconvexity facing to the object side and a concave lens with a strongconcavity facing to an image side, which are disposed in order from theobject side, and at least one surface is an aspheric surface; and thefourth lens group is composed of a single convex lens, and at least onesurface is an aspheric surface, and characterized by satisfying each ofthe following conditional expressions (9) and (10):0.4<h3-5/h3-1<0.7;  (9)and0.75<f3/f3-1<1,  (10) where: h3-i is a paraxial ray height in the i-thsurface from the object side of the third lens group, when allowing aparaxial ray parallel to an optical axis to enter the first lens groupat a wide angle end; f3 is a focal length of the third lens group; andf3-1 is a focal length of the single convex lens of the third lensgroup.
 6. The zoom lens as claimed in claim 2, characterized in that:the third lens group is composed of a convex lens, and a cemented lensmade up of a convex lens with a strong convexity facing to an objectside and a concave lens with a strong concavity facing to an image side,which are disposed in order from the object side, and at least onesurface is an aspheric surface; and the fourth lens group is composed ofa single convex lens, and at least one surface is an aspheric surface,and characterized by satisfying each of the following conditionalexpressions (9) and (10):0.4<h3-5/h3-1<0.7;  (9)and0.75<f3/f3-1<1,  (10) where: h3-i is a paraxial ray height in the i-thsurface from the object side of the third lens group, when allowing aparaxial ray parallel to an optical axis to enter the first lens groupat a wide angle end; f3 is a focal length of the third lens group; andf3-1 is a focal length of the single convex lens of the third lensgroup.
 7. The zoom lens as claimed in claim 1, characterized in that:the third lens group is composed of a single convex lens, and at leastone surface is an aspheric surface; and the fourth lens group iscomposed of a cemented lens made up of a convex lens with a convexityfacing to the object side, a concave lens, and a convex lens, which aredisposed in order from the object side, and at least a surface closestto the object side is an aspheric surface, and characterized bysatisfying each of the following conditional expressions (11) and (12):n4-2>1.8;  (11)and0.1<f3/f4<0.7,  (12) where: n4-2 is a refractive index on a d-line ofthe concave lens of the fourth lens group; f3 is a focal length of thethird lens group; and f4 is a focal length of the fourth lens group. 8.The zoom lens as claimed in claim 2, characterized in that: the thirdlens group is composed of a single convex lens, and at least one surfaceis an aspheric surface; and the fourth lens group is composed of acemented lens made up of a convex lens with a convexity facing to theobject side, a concave lens, and a convex lens, which are disposed inorder from the object side, and at least a surface closest to the objectside is an aspheric surface, and characterized by satisfying each of thefollowing conditional expressions (11) and (12):n4-2>1.8;  (11)and0.1<f3/f4<0.7,  (12) where: n4-2 is a refractive index on a d-line ofthe concave lens of the fourth lens group; f3 is a focal length of thethird lens group; and f4 is a focal length of the fourth lens group. 9.The zoom lens as claimed in claim 1, characterized in that: the thirdlens group is composed of a convex lens and a cemented lens made up of aconvex lens with a strong convexity facing to the object side and aconcave lens with a strong concavity facing to the image side, which aredisposed in order from the object side, and at least one surface is anaspheric surface; and the fourth lens group is composed of a cementedlens made up of a double convex lens and a concave lens with a convexityfacing to the image side, and at least one surface is an asphericsurface, and characterized by satisfying each of the followingconditional expressions (9), (11), and (13):0.4<h3-5/h3-1<0.7;  (9)n4-2>1.8;  (11)and0.75<f3/f3-1<1.3,  (13) where: h3-i is a paraxial ray height in the i-thsurface from the object side of the third lens group, when allowing aparaxial ray parallel to an optical axis to enter the first lens groupat a wide angle end; f3 is a focal length of the third lens group; f3-1is a focal length of the single convex lens of the third lens group; andn4-2 is a refractive index on a d-line of the concave lens of the fourthlens group.
 10. The zoom lens as claimed in claim 2, characterized inthat: the third lens group is composed of a convex lens and a cementedlens made up of a convex lens with a strong convexity facing to theobject side and a concave lens with a strong concavity facing to theimage side, which are disposed in order from the object side, and atleast one surface is an aspheric surface; and the fourth lens group iscomposed of a cemented lens made up of a double convex lens and aconcave lens with a convexity facing to the image side, and at least onesurface is an aspheric surface, and characterized by satisfying each ofthe following conditional expressions (9), (11), and (13):0.4<h3-5/h3-1<0.7;  (9)n4-2>1.8;  (11)and0.75<f3/f3-1<1.3  (13) where: h3-i is a paraxial ray height in the i-thsurface from the object side of the third lens group, when allowing aparaxial ray parallel to an optical axis to enter the first lens groupat a wide angle end; f3 is a focal length of the third lens group; f3-1is a focal length of the single convex lens of the third lens group; andn4-2 is a refractive index on a d-line of the concave lens of the fourthlens group.
 11. An image pickup apparatus including: a zoom lens; imagepickup means for converting an image captured by the zoom lens into anelectric image signal; and image control means, characterized in that:said image control means is configured so as to form a new image signalsubjected to coordinate conversion by shifting a point on an imagedefined by an image signal formed by said image pickup means, whilereferring to a conversion coordinate factor previously provided inresponse to a variable power rate through said zoom lens, and output thenew image signal; said zoom lens is composed of a first lens grouphaving positive refracting power, a second lens group having negativerefracting power, a third lens group having positive refracting power,and a fourth lens group having positive refracting power, which aredisposed in order from the object side, in which the first lens groupand the third lens group are stationary, and the zoom lens performsmainly variable power by shifting the second lens group in an opticalaxis direction, and performs correction for image position fluctuationsand focusing by shifting the fourth lens group in the optical axisdirection; and said first lens group is composed of five lenses: aconcave lens; a convex lens with a strong convexity facing to an imageside; a cemented lens made up of a concave lens with a strong concavityfacing to the image side, and a convex lens; and a convex lens with astrong convexity facing to the object side, which are disposed in orderfrom the object side, and is characterized by satisfying each of thefollowing conditional expressions:(1) 1.25<h1-4/h1-1<1.55;(2) 1-2/d1-3<0.4;(3) 1.65<n1-2;and(4) 0.1<H1′/f1<0.6, where: f1 is a focal length of the first lens group;h1-i is a paraxial ray height in the i-th surface from the object sidewhen allowing a paraxial ray parallel to an optical axis to enter thefirst lens group; d1-i is axial spacing from the i-th surface to the(i+1)-th surface in the first lens group; n1-i is a refractive index ona d-line of the i-th lens in the first lens group; and H1′ is spacingfrom a vertex of a surface closest to the image side in the first lensgroup to a principal point on the image side in the first lens group(“−” indicates the object side, and “+” indicates the image side). 12.The image pickup apparatus as claimed in claim 11, characterized inthat: the second lens group of said zoom lens is composed of threelenses of a concave meniscus lens with a strong concavity facing to theimage side, a double concave lens, and a convex lens, which are disposedin order from the object side, and satisfies the following conditionalexpression (5):1.8<(n2-1+n2-2)/2,  (5) where: n2-1 is a refractive index on a d-line ofthe concave meniscus lens of the second lens group; and n2-2 is arefractive index on a d-line of the double concave lens of the secondlens group.
 13. The image pickup apparatus as claimed in claim 11,characterized in that: the third lens group of said zoom lens iscomposed of a single convex lens, and at least one surface is anaspheric surface; and the fourth lens group of said zoom lens iscomposed of a cemented lens made up of a concave meniscus lens with aconcavity facing to the image side, and a double convex lens whosesurface on the image side is an aspheric surface, which are disposed inorder from the object side, and characterized by satisfying each of thefollowing conditional expressions (6), (7), and (8):−0.4<f3/r3-2<0.4;  (6)−1.25<r4-1/r4-3<−0.8;  (7)and0.3<r4-2/f4<0.6,  (8) where: f3 is a focal length of the third lensgroup; f4 is a focal length of the fourth lens group; r3-2 is a radiusof curvature of the image side surface of the convex lens of the thirdlens group; r4-1 is a radius of curvature of the object side surface ofthe concave meniscus lens of the fourth lens group; r4-2 is a radius ofcurvature of a cemented surface of the fourth lens group; and r4-3 is aradius of curvature of a surface on the image side of the convex lens ofthe fourth lens group.
 14. The image pickup apparatus as claimed inclaim 12, characterized in that: the third lens group of said zoom lensis composed of a single convex lens, and at least one surface is anaspheric surface; and the fourth lens group of said zoom lens iscomposed of a cemented lens made up of a concave meniscus lens with aconcavity facing to the image side, and a double convex lens whosesurface on the image side is an aspheric surface, which are disposed inorder from the object side, and characterized by satisfying each of thefollowing conditional expressions (6), (7), and (8):−0.4<f3/r3-2<0.4;  (6)−1.25<r4-1/r4-3<−0.8;  (7)and0.3<r4-2/f4<0.6,  (8) where: f3 is a focal length of the third lensgroup; f4 is a focal length of the fourth lens group; r3-2 is a radiusof curvature of the image side surface of the convex lens of the thirdlens group; r4-1 is a radius of curvature of the object side surface ofthe concave meniscus lens of the fourth lens-group; r4-2 is a radius ofcurvature of a cemented surface of the fourth lens group; and r4-3 is aradius of curvature of a surface on the image side of the convex lens ofthe fourth lens group.
 15. The image pickup apparatus as claimed inclaim 11, characterized in that: the third lens group of said zoom lensis composed of a convex lens, and a cemented lens made up of a convexlens with a strong convexity facing to the object side, and a concavelens with a strong concavity facing to an image side, which are disposedin order from the object side, and at least one surface is an asphericsurface; and the fourth lens group of said zoom lens is composed of asingle convex lens, and at least one surface is an aspheric surface, andcharacterized by satisfying each of the following conditionalexpressions (9) and (10):0.4<h3-5/h3-1<0.7;  (9)and0.75<f3/f3-1<1,  (10) where: h3-i is a paraxial ray height in the i-thsurface from the object side of the third lens group, when allowing aparaxial ray parallel to an optical axis to enter the first lens groupat a wide angle end; f3 is a focal length of the third lens group; andf3-1 is a focal length of the single convex lens of the third lensgroup.
 16. The image pickup apparatus as claimed in claim 12,characterized in that: the third lens group of said zoom lens iscomposed of a convex lens, and a cemented lens made up of a convex lenswith a strong convexity facing to the object side, and a concave lenswith a strong concavity facing to an image side, which are disposed inorder from the object side, and at least one surface is an asphericsurface; and the fourth lens group of said zoom lens is composed of asingle convex lens, and at least one surface is an aspheric surface, andcharacterized by satisfying each of the following conditionalexpressions (9) and (10):0.4<h3-5/h3-1<0.7;  (9)and0.75<f3/f3-1<1,  (10) wherein: h3-i is a paraxial ray height in the i-thsurface from the object side of the third lens group, when allowing aparaxial ray parallel to an optical axis to enter the first lens groupat a wide angle end; f3 is a focal length of the third lens group; andf3-1 is a focal length of the single convex lens of the third lensgroup.
 17. The image pickup apparatus as claimed in claim 11,characterized in that: the third lens group of said zoom lens iscomposed of a single convex lens, and at least one surface is anaspheric surface; and the fourth lens group of said zoom lens iscomposed of a cemented lens made up of a convex lens with a convexityfacing to an object side, a concave lens, and a convex lens, which aredisposed in order from the object side, and at least a surface closestto the object side is an aspheric surface, and characterized bysatisfying each of the following conditional expressions (11) and (12):n4-2>1.8;  (11)and0.1<f3/f4<0.7,  (12) where: n4-2 is a refractive index on a d-line ofthe concave lens of the fourth lens group; f3 is a focal length of thethird lens group; and f4 is a focal length of the fourth lens group. 18.The image pickup apparatus as claimed in claim 12, characterized inthat: the third lens group of said zoom lens is composed of a singleconvex lens, and at least one surface is an aspheric surface; and thefourth lens group of said zoom lens is composed of a cemented lens madeup of a convex lens with a convexity facing to an object side, a concavelens, and a convex lens, which are disposed in order from the objectside, and at least a surface closest to the object side is an asphericsurface, and characterized by satisfying each of the followingconditional expressions (11) and (12):n4-2>1.8;  (11)and0.1<f3/f4<0.7,  (12) where: n4-2 is a refractive index on a d-line ofthe concave lens of the fourth lens group; f3 is a focal length of thethird lens group; and f4 is a focal length of the fourth lens group. 19.The image pickup apparatus as claimed in claim 11, characterized inthat: the third lens group of said zoom lens is composed of a convexlens and a cemented lens made up of a convex lens with a strongconvexity facing to the object side and a concave lens with a strongconcavity facing to the image side, which are disposed in order from theobject side, and at least one surface is an aspheric surface; and thefourth lens group of said zoom lens is composed of a cemented lens madeup of a double convex lens and a concave lens with a convexity facing tothe image side, and at least one surface is an aspheric surface, andcharacterized by satisfying each of the following conditionalexpressions (9), (11), and (13):0.4<h3-5/h3-1<0.7;  (9)n4-2>1.8;  (11)and0.75<f3/f3-1<1.3,  (13) where: h3-i is a paraxial ray height in the i-thsurface from the object side of the third lens group, when allowing aparaxial ray parallel to an optical axis to enter the first lens groupat a wide angle end; f3 is a focal length of the third lens group; f3-1is a focal length of the single convex lens of the third lens group; andn4-2 is a refractive index on a d-line of the concave lens of the fourthlens group.
 20. The image pickup apparatus according to claim 12,characterized in that: the third lens group of said zoom lens iscomposed of a convex lens and a cemented lens made up of a convex lenswith a strong convexity facing to the object side and a concave lenswith a strong concavity facing to the image side, which are disposed inorder from the object side, and at least one surface is an asphericsurface; and the fourth lens group of said zoom lens is composed of acemented lens made up of a double convex lens and a concave lens with aconvexity facing to the image side, and at least one surface is anaspheric surface, characterized by satisfying each of the followingconditional expressions (9), (11), and (13):0.4<h3-5/h3-1<0.7;  (9)n4-2>1.8;  (11)and0.75<f3/f3-1<1.3,  (13) where: h3-i is a paraxial ray height in the i-thsurface from the object side of the third lens group, when allowing aparaxial ray parallel to an optical axis to enter the first lens groupat a wide angle end; f3 is a focal length of the third lens group; f3-1is a focal length of the single convex lens of the third lens group; andn4-2 is a refractive index on a d-line of the concave lens of the fourthlens group.